>>7078471Links are necessary if you want to have more than 1 of those great extra deck monsters on your side of the field at a time.
I'll give an example, lets say you manage to summon a strong monster from your extra deck like pic related. its effect allows you to summon 2 tokens to serve as weak monsters. Before link summoning you'd be in a good position, activating Dracosack's effect protects it as long as you have the tokens. You opponent will have to spend precious resources getting rid of the tokens because next turn you could summon another monster and use it with those tokens to summon a different monster from your extra deck. Your opponent would be in a dire spot because now you have 2 powerful extra deck monsters against him.
But with the new rules, if you summon pic related and you don't have a link monster on the field already, you can't use the summoned tokens to go for another extra deck monster because you can only have 1 non-link extra deck monster on the field at a time if you don't control a link monster. Said link monster is usually just as difficult to summon as dracosack, so by the time you summon the link monster and then dracosack you've spent a lot of resources (cards) and probably overextended yourself. If you opponent does anything at all to interrupt your plays it will be very difficult to get back on your feet, which was not the case before links.
Sorry if this was a long post, I hope this helps with understanding.
